build error: undefined symbol: __kmpc_fork_call, __kmpc_for_static_init_4u, __kmpc_for_static_fini

[miyanyan]

platform:
win11, clang-cl
openmp version: 5.1

error:

build] LINK: command "C:\PROGRA~1\MICROS~1\2022\COMMUN~1\VC\Tools\Llvm\x64\bin\lld-link.exe /nologo examples\CMakeFiles\fps.dir\fps.cpp.obj /out:examples\fps.exe /implib:examples\fps.lib /pdb:examples\fps.pdb /version:0.0 /machine:x64 /INCREMENTAL:NO /subsystem:console opengl32.lib D:\github\miyanyan\vcpkg\installed\x64-windows\lib\glfw3dll.lib D:\github\miyanyan\vcpkg\installed\x64-windows\lib\freetype.lib kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib /MANIFEST:EMBED,ID=1" failed (exit code 1) with the following output:
[build] lld-link: error: undefined symbol: __kmpc_fork_call
[build] >>> referenced by examples\CMakeFiles\fps.dir\fps.cpp.obj:(main)
[build] 
[build] lld-link: error: undefined symbol: __kmpc_for_static_init_4u
[build] >>> referenced by examples\CMakeFiles\fps.dir\fps.cpp.obj:(main.omp_outlined)
[build] 
[build] lld-link: error: undefined symbol: __kmpc_for_static_fini
[build] >>> referenced by examples\CMakeFiles\fps.dir\fps.cpp.obj:(main.omp_outlined)

another error:

[build] LINK: command "C:\PROGRA~1\MICROS~1\2022\COMMUN~1\VC\Tools\Llvm\x64\bin\lld-link.exe /nologo examples\CMakeFiles\hexgrid_image_rect.dir\hexgrid_image_rect.cpp.obj /out:examples\hexgrid_image_rect.exe /implib:examples\hexgrid_image_rect.lib /pdb:examples\hexgrid_image_rect.pdb /version:0.0 /machine:x64 /INCREMENTAL:NO /subsystem:console opengl32.lib D:\github\miyanyan\vcpkg\installed\x64-windows\lib\glfw3dll.lib D:\github\miyanyan\vcpkg\installed\x64-windows\lib\freetype.lib kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib /MANIFEST:EMBED,ID=1" failed (exit code 1) with the following output:
[build] lld-link: error: undefined symbol: __kmpc_fork_call
[build] >>> referenced by examples\CMakeFiles\hexgrid_image_rect.dir\hexgrid_image_rect.cpp.obj:(public: struct sm::vvec<float, class std::allocator<float>> __cdecl sm::hexgrid::resampleImage(struct sm::vvec<float, class std::allocator<float>> const &, unsigned int, struct sm::vec<float, 2> const &, struct sm::vec<float, 2> const &))
[build] 
[build] lld-link: error: undefined symbol: __kmpc_for_static_init_8u
[build] >>> referenced by examples\CMakeFiles\hexgrid_image_rect.dir\hexgrid_image_rect.cpp.obj:(public: struct sm::vvec<float, class std::allocator<float>> __cdecl sm::hexgrid::resampleImage(struct sm::vvec<float, class std::allocator<float>> const &, unsigned int, struct sm::vec<float, 2> const &, struct sm::vec<float, 2> const &))
[build] 
[build] lld-link: error: undefined symbol: __kmpc_for_static_fini
[build] >>> referenced by examples\CMakeFiles\hexgrid_image_rect.dir\hexgrid_image_rect.cpp.obj:(public: struct sm::vvec<float, class std::allocator<float>> __cdecl sm::hexgrid::resampleImage(struct sm::vvec<float, class std::allocator<float>> const &, unsigned int, struct sm::vec<float, 2> const &, struct sm::vec<float, 2> const &))
[build] [18/124   4% :: 0.294] Linking CXX executable examples\hexgrid_image_onsphere.exe
[build] FAILED: examples/hexgrid_image_onsphere.exe 

[miyanyan]

mathplot/examples/CMakeLists.txt

Lines 61 to 66 in 491de1a

	add_executable(fps fps.cpp)
	if(APPLE AND OpenMP_CXX_FOUND)
	target_link_libraries(fps OpenMP::OpenMP_CXX OpenGL::GL glfw Freetype::Freetype)
	else()
	target_link_libraries(fps OpenGL::GL glfw Freetype::Freetype)
	endif()

seems doesn't link openmp

[sebsjames]

This if(APPLE AND... statement shows how on Apple, when using OpenMP, I found it necessary to link libomp. On Linux when compiling with gcc or clang and using OpenMP, it is not necessary to link to libomp unless using functions that I have avoided in my code.

I probably didn't compile with OpenMP on Windows before, so you are discovering new requirements for compiling with clang-cl on Windows 11. Feel free to create a PR to add suitable links for OpenMP on your platform.

[miyanyan]

I tried on linux, seems it links openmp by default, and linking it in cmake manually behaves the same

ldd fps
        linux-vdso.so.1 (0x00007ffd7c75b000)
        libglfw.so.3 => /lib/x86_64-linux-gnu/libglfw.so.3 (0x00007e89ea650000)
        libfreetype.so.6 => /lib/x86_64-linux-gnu/libfreetype.so.6 (0x00007e89ea584000)
        libgomp.so.1 => /lib/x86_64-linux-gnu/libgomp.so.1 (0x00007e89ea52e000)
        libstdc++.so.6 => /lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007e89ea200000)
        libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007e89ea117000)
        libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007e89ea4fe000)
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007e89e9e00000)
        libX11.so.6 => /lib/x86_64-linux-gnu/libX11.so.6 (0x00007e89e9cc3000)
        libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007e89ea4e2000)
        libbz2.so.1.0 => /lib/x86_64-linux-gnu/libbz2.so.1.0 (0x00007e89ea4ce000)
        libpng16.so.16 => /lib/x86_64-linux-gnu/libpng16.so.16 (0x00007e89ea496000)
        libbrotlidec.so.1 => /lib/x86_64-linux-gnu/libbrotlidec.so.1 (0x00007e89ea486000)
        /lib64/ld-linux-x86-64.so.2 (0x00007e89eaadb000)
        libxcb.so.1 => /lib/x86_64-linux-gnu/libxcb.so.1 (0x00007e89ea0ee000)
        libbrotlicommon.so.1 => /lib/x86_64-linux-gnu/libbrotlicommon.so.1 (0x00007e89ea0cb000)
        libXau.so.6 => /lib/x86_64-linux-gnu/libXau.so.6 (0x00007e89ea480000)
        libXdmcp.so.6 => /lib/x86_64-linux-gnu/libXdmcp.so.6 (0x00007e89ea0c3000)
        libbsd.so.0 => /lib/x86_64-linux-gnu/libbsd.so.0 (0x00007e89ea0ad000)
        libmd.so.0 => /lib/x86_64-linux-gnu/libmd.so.0 (0x00007e89ea09e000)

so what about linking openmp in cmake on all platforms, this makes the code simple

 add_executable(fps fps.cpp)
 target_link_libraries(fps OpenMP::OpenMP_CXX OpenGL::GL glfw Freetype::Freetype)

[sebsjames]

Ah, so it does. I thought that on Linux you didn't need to link libomp (or in this case libgomp) unless you used certain features of OpenMP. However, it seems that gcc is also linking to libgomp on this link call, which has the flag -fopenmp:

Linking CXX executable fps
cd /home/seb/src/mathplot/build/examples && /usr/local/bin/cmake -E cmake_link_script CMakeFiles/fps.dir/link.txt --verbose=1
/usr/bin/c++ -g -Wall -Wextra -Wpedantic -pedantic-errors -Werror -Wfatal-errors -Wno-psabi -O3 -fconstexpr-ops-limit=5000000000 -DMPLOT_HAVE_STD_FORMAT -fopenmp -DMPLOT_FONTS_DIR="\"/home/seb/src/mathplot/fonts\""  CMakeFiles/fps.dir/fps.cpp.o -o fps  /usr/lib/x86_64-linux-gnu/libglfw.so.3.3 /usr/lib/x86_64-linux-gnu/libfreetype.so /usr/lib/x86_64-linux-gnu/libGLX.so /usr/lib/x86_64-linux-gnu/libOpenGL.so 

So I'm happy to do what you suggest